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Nordic
2015 Nordic
1
1
Part of
2015 Nordic
Problems
(1)
circle with diameter a side of a triangle
Source: Nordic Mathematical Contest 2015 #1
9/23/2017
Let
A
B
C
{ABC}
A
BC
be a triangle and
Γ
{\Gamma}
Γ
the circle with diameter
A
B
{AB}
A
B
. The bisectors of
∠
B
A
C
{\angle BAC}
∠
B
A
C
and
∠
A
B
C
{\angle ABC}
∠
A
BC
intersect
Γ
{\Gamma}
Γ
(also) at
D
{D}
D
and
E
{E}
E
, respectively. The incircle of
A
B
C
{ABC}
A
BC
meets
B
C
{BC}
BC
and
A
C
{AC}
A
C
at
F
{F}
F
and
G
{G}
G
, respectively. Prove that
D
,
E
,
F
{D, E, F}
D
,
E
,
F
and
G
{G}
G
are collinear.
geometry